1. Field of the Invention
This invention relates to a molded surface fastener having a multiplicity of engaging elements formed on one surface of a substrate sheet by injection or extrusion using thermoplastic resin and a method of manufacturing the surface fastener. More particularly, the invention relates to a molded surface fastener in which a substrate sheet can be torn along and between a desired adjacent pair of rows of male engaging elements and a method of manufacturing the surface fastener.
2. Description of the Related Art
A conventional type surface fastener in which a substrate sheet and engaging elements to be formed on one surface of the substrate sheet are integrally molded by extrusion and in which a backing strip is attached to the substrate sheet during molding is disclosed in, for example, U.S. Pat. No. 5,260,015. According to this U.S. Patent, molten thermoplastic resin is extruded toward a predetermined gap between a drum-shape die wheel, which is composed of a plurality of mold disc and a plurality of spacer plates alternately placed one over another, and a press roller and, at the same time, the backing strip is introduced between the extruded resin and the press roller. As the backing strip is introduced, part of the resin is penetrated into the backing strip under the pressure by the press roller and at the same time, hook-element-forming cavities in the circumferential surface of the die wheel are filled with part of the resin to mold hook elements. The resulting surface fastener wits the backing strip integrally attached to a surface opposite-to the surface having the hook elements of the substrate sheet is cooled as it is moved around the circumferential surface of the die wheel through a predetermined angle along the rotation of the die wheel, whereupon the molded hook elements are pulled off the cavities as the substrate sheet is continuously removed from the circumferential surface of the die wheel.
In the meantime, the present inventors have made copending U.S. patent application, Ser. No. 08/359,895, on a continuous injection molding method for continuously manufacturing a surface fastener having yarns embedded in a substrate sheet. According to this U.S. patent application, molten resin is continuously injected from an injection die, which is disposed in confronting relationship with a die wheel with a predetermined gap therebetween having in the circumferential surface a multiplicity of engaging-element-forming cavities and having inside a cooling means, to the circumferential surface of the die wheel, by a predetermined width and at the same time, a plurality of yarns are continuously introduced in the direction of rotation of the die wheel circumferentially thereof so as to cross an outlet of the injected molten resin while one or more yarns are introduced as being traversed by a predetermined width in parallel to the axis of the die wheel. As the engaging-element-forming cavities are filled with part of the molten resin, the die wheel is driven to rotate simultaneously with injection of the molten resin to embed the yarns in the substrate sheet and at the same time, to integrally mold a multiplicity of engaging elements on the surface of substrate sheet. The molded and cooled surface fastener is moved about the circumferential surface of the die wheel through a predetermined angle along the rotation of the die wheel, whereupon the substrate sheet together with the engaging elements are positively pulled off the circumferential surface of the die wheel.
According to the method disclosed in U.S. Pat. No. 5,260,015, in order to overcome a difficulty that when a rear surface of the surface fastener of this conventional type is smooth, an adhesive agent or cement cannot be easily applied unless the surface is given some special treatment, an object is to make it easier to apply the adhesive agent or cement to the smooth back surface of the surface fastener by integrally attaching a backing strip or to form a multiplicity of piles as female engaging elements on the back surface of the substrate sheet using the backing strip.
On the other hand, according to the method disclosed in U.S. patent application, Ser. No. 08/359,895, the yarns are introduced in a meandering manner to the circumferential surface of the die wheel in order to reinforce the substrate sheet, and in the presence of added yarns traversed across the circumferential surface of the die wheel, the substrate sheet can be reinforced more.
In either of these two methods, from a manufacturing efficiency view point, a large-width surface fastener is molded and is then divided into desired-width surface fasteners by cutting, whereupon the small-width surface fasteners are delivered from the factory. On many occasions, however, such surface fastener has to be further divided into ones with narrower width at retailer shops, sewing factories, or other working cites. Consequently it has been inevitable to cut the large-width surface fastener along and between a desired pair of rows of male engaging elements into desired small-width surface fasteners by cutting means such as scissors. If the substrate sheet has a thickness exceeding 0.25 mm, this type molded surface fastener cannot be torn unless it is torn by a pulling force larger than 1 kg.